LITHIUM TOXICITY AND NA+(LI+) H+ ANTIPORTER IN ESCHERICHIA-COLI/

The lithium ion (Li+) shows toxicity against Escherichia coli cells wh en present in a high concentration in the environment. Since Li+ is ex truded from cells via a Na+(Li+)/H+ antiporter, this antiporter must b e involved in the detoxification of Li+. Two Na+(Li+)/H+ antiporters ( NhaA system and NhaB system) are known to be present in E. coli. We in vestigated the properties of the antiporters and the participation of these systems in the detoxification of Li+ using mutants lacking one o f the antiporters, or lacking both of them. Although the affinity for Li+ of the two systems was almost the same, the V(max), value for Litransport of the NhaA system was about 12 times larger than that of th e NhaB system. Wild type cells were unable to grow in the presence of 0.7 M LiCl. Although a wild type cell and a mutant lacking the NhaB sy stem grew in the presence of 0.6 M LiCl, a mutant lacking the NhaA sys tem did not. This second mutant grew in the presence of 0.1 to 0.2 M L iCl. A mutant lacking both the NhaA and NhaB systems could not grow in the presence of 30 mM LiCl.